Effects of weather variability and geese on population dynamics of large herbivores creating opportunities for wood-pasture cycles : A modelling approach

(chapter 7 of PhD thesis) Coexistence of large herbivores and vegetation heterogeneity is a challenge for managers of relatively small and homogeneous nature reserves in fragmented landscapes. A modelling analysis was performed to study if observed variability in weather conditions would be of sufficient magnitude to maintain long-term coexistence of large herbivore species, and to provide windows of opportunity for the establishment of thorny shrubs as predicted by the wood-pasture hypothesis. The study was applied to the Oostvaardersplassen nature reserve in the Netherlands, which has a large herbivore assemblage of Heck cattle, Konik horse and red deer. Owing to the fact that a large number of geese frequent the nature reserve, the effects of these small herbivores were taken into account in the model analyses. The results showed that weather variability increases population fluctuations and that geese reduce large herbivore numbers. The results also indicated that coexistence of the three large herbivore species is possible irrespective of weather variability and geese. However, the chances for the coexistence of cattle with the other large herbivores are reduced when weather is highly variable and geese numbers are high. If the management of large nature reserves aims at natural processes with assemblages of self-regulating large herbivore populations, our results show that weather variability and the presence of small competing herbivores may be essential factors in highly productive environments for the wood-pasture cycle creating a more heterogeneous landscape.